Since PG's exhibit various important biological effects in a trace amount, investigations have been made of the synthesis and biological activity of natural PG's and a large number of PG analogues with the intention of use as medicines.
Especially, PGE.sub.1 is now commercially available as a drug for the improvement of peripheral circulatory disturbances because of having characteristic effects such as blood platelet aggregation inhibiting effect and blood pressure reducing effect, and therefore, a large number of PGE.sub.1 analogues have also been studied. However, the prior art PGE.sub.1 analogues are quickly metabolized in vivo and thereby have drawbacks such as lack of duration of the effect. Furthermore, the prior art PGE.sub.1 analogues cannot be administered orally in a sufficiently high amount to obtain the satisfactory effects because of causing diarrhea as a side-effect.
On the other hand, the known 13, 14-didehydro PGE.sub.1 analogues in which the double bond between the 13- and 14-positions of PGE.sub.1 is replaced by a triple bond include 13,14-didehydro PGE.sub.1 methyl ester and 6-hydroxy-13,14-didehydro PGE.sub.1.
An object of the present invention is to provide novel PGE.sub.1 analogues which have more excellent pharmaceutical effects, longer duration of the effect and less side-effects than the prior art PGE.sub.1 analogues.